The invention relates to heat treatable coated glass panes with a low-e and/or solar control coating. The invention also relates to methods of manufacturing said panes.
Heat treated glass panes which are toughened to impart safety properties and/or are bent are required for a large number of areas of application, for example for architectural or motor vehicle glazings. It is known that for thermally toughening and/or bending glass panes it is necessary to process the glass panes by a heat treatment at temperatures near or above the softening point of the glass used and then either to toughen them by rapid cooling or to bend them with the aid of bending means. The relevant temperature range for standard float glass of the soda lime silica type is typically about 580-690° C., the glass panes being kept in this temperature range for several minutes before initiating the actual toughening and/or bending process.
“Heat treatment”, “heat treated” and “heat treatable” in the following description and in the claims refer to thermal bending and/or toughening processes such as mentioned before and to other thermal processes during which a coated glass pane reaches temperatures in the range of about 580-690° C. for a period of several minutes, e.g., for up to about 10 minutes. A coated glass pane is deemed to be heat treatable if it survives a heat treatment without significant damage, typical damages caused by heat treatments being high haze values, pinholes or spots.
US2009/0197077 describes glass successively coated with at least one dielectric layer based on aluminum and/or silicon nitride, at least one non-crystallised mixed oxide smoothing layer such as ZnSnOx:Sb, a wetting layer e.g. ZnO, a silver based functional layer, a blocker layer for instance NiCr- or Ti-based, a layer of ZnO and a layer of aluminum and/or silicon nitride. The coated glass is said to exhibit reduced sheet resistance.
WO 2010/073042 describes chemically and mechanically robust heat treatable coated glass panes with low-e and/or solar control coatings comprising in sequence from the glass pane a lower anti-reflection layer of a base layer of an (oxi)nitride of silicon having a thickness of at least 8 nm, a middle layer of an oxide of Zn and Sn, and a top layer of a metal oxide; a silver-based functional layer; a barrier layer; and an upper anti-reflection layer comprising a layer of an (oxi)nitride of aluminum having a thickness of more than 10 nm.
DE 19922162 A1 describes a transparent layer system, especially a heat insulating and solar protection coating for glazing, which has a thin metal or metal compound modification layer between two base layers in the lower dielectric. Metals or substoichiometric oxides or nitrides are used for the modification layer, but oxides and nitrides have been found to not provide the desired improvement in optical properties.
It is well known to use substoichiometric NiCrOx as a sacrificial barrier layer (e.g. see US2009/0197077 and WO 2010/073042) since it affords favourable heat treatability. However, the presence of a NiCrOx layer complicates manufacturing because of the critical conditions required to deposit a layer of the correct stoichiometry. The use of NiCrOx furthermore leads to significant changes of optical properties, i.e. light transmittance, colour, absorption, light reflectance of the coating stack during a heat treatment that makes it difficult to achieve a single stock coated glass pane, i.e. a coated glass pane having essentially the same optical properties with and without a heat treatment. Therefore it would be attractive to provide a coated glass pane that can exhibit a neutral reflection colour (colourless) and low haze before and after toughening. It would also be desirable to provide a coated glass pane that exhibits less change in percentage light transmittance (ΔTL) and reflection colour (Δa*, Δb*) upon toughening. Accordingly, a coated glass pane that affords these optical benefits alongside good heat treatability, without the need for a substoichiometric NiCrOx sacrificial barrier layer above the silver-based functional layer, is sought after.
The inventors of the instant invention found that the parameter “haze” usually referred to when characterising the heat treatability of low-e and/or solar control coatings is often insufficient, as it does not fully reflect all types of defects that may arise during coating, heat treating, processing and/or handling of coated glass panes. They found that several low-e and/or solar control coated glass described as heat treatable did not withstand without visible damage one or the other test simulating ordinary environmental influences during storage, transport and use of the coated glass panes before and after a heat treatment and the mechanical and chemical conditions acting on the coated glass panes during usual handling and processing steps. Certain of the known heat treatable coated glass panes showed significant and clearly noticeable modifications of their optical properties and particularly of their reflection colour during a heat treatment.
A “single stock coated glass pane” as referred to in the present application is defined as a pane that upon heat treatment exhibits a ΔTL≦2%, preferably ΔTL≦1.5% (where ΔTL is the change in % light transmittance upon heat treatment), with a Rf ΔE*≦3, preferably Rf ΔE*≦2 (where the change in film side reflection colour upon heat treatment, Rf ΔE*=SQR[L*1−L*2)2+(a*1−a*2)2+(b*1−b*2)2], L*i, a*i and b*i being the film side reflection colour values before and after heat treatment). The colour change, ΔE*, is defined by 1976 CIE (L*a*b*) with illuminant D65 and 10° observer.